Description: fix race condition allowing attackers to access destination file
 This commit addresses https://github.com/facebook/zstd/issues/2491.
 .
 Note that a downside of this solution is that it is global: `umask()` affects
 all file creation calls in the process. I believe this is safe since
 `fileio.c` functions should only ever be used in the zstd binary, and these
 are (almost) the only files ever created by zstd, and AIUI they're only
 created in a single thread. So we can get away with messing with global state.
 .
 Note that this doesn't change the permissions of files created by `dibio.c`.
 I'm not sure what those should be...
Author: W. Felix Handte <w@felixhandte.com>
Origin: upstream
Bug: https://github.com/facebook/zstd/issues/2491
Bug-Debian: https://github.com/facebook/zstd/issues/2491
Applied-Upstream: commit:a774c5797399040af62db21d8a9b9769e005430e
Reviewed-by: Étienne Mollier <etienne.mollier@mailoo.org>
Last-Update: 2021-03-03
---
This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
--- a/programs/fileio.c
+++ b/programs/fileio.c
@@ -606,11 +606,11 @@ FIO_openDstFile(FIO_prefs_t* const prefs
             FIO_remove(dstFileName);
     }   }
 
-    {   FILE* const f = fopen( dstFileName, "wb" );
+    {   const int old_umask = UTIL_umask(0177); /* u-x,go-rwx */
+        FILE* const f = fopen( dstFileName, "wb" );
+        UTIL_umask(old_umask);
         if (f == NULL) {
             DISPLAYLEVEL(1, "zstd: %s: %s\n", dstFileName, strerror(errno));
-        } else if(srcFileName != NULL && strcmp (srcFileName, stdinmark)) {
-            chmod(dstFileName, 00600);
         }
         return f;
     }
--- a/programs/util.c
+++ b/programs/util.c
@@ -54,6 +54,15 @@ int UTIL_getFileStat(const char* infilen
     return 1;
 }
 
+int UTIL_umask(int mode) {
+#if PLATFORM_POSIX_VERSION > 0
+    return umask(mode);
+#else
+    /* do nothing, fake return value */
+    return mode;
+#endif
+}
+
 int UTIL_setFileStat(const char *filename, stat_t *statbuf)
 {
     int res = 0;
--- a/programs/util.h
+++ b/programs/util.h
@@ -136,6 +136,10 @@ int UTIL_isSameFile(const char* file1, c
 int UTIL_compareStr(const void *p1, const void *p2);
 int UTIL_isCompressedFile(const char* infilename, const char *extensionList[]);
 const char* UTIL_getFileExtension(const char* infilename);
+/**
+ * Wraps umask(). Does nothing when the platform doesn't have that concept.
+ */
+int UTIL_umask(int mode);
 
 #ifndef _MSC_VER
 U32 UTIL_isFIFO(const char* infilename);
